A biofilm infection is a type of infection caused by an aggregated community of microorganisms that adhere onto the surface of animate or inanimate objects. For example, native human tissue can serve as an animate surface whereas implanted medical devices can serve as inanimate surfaces. A biofilm can be mono- or polymicrobial and can be prokaryotic, eukaryotic, or both.
During the formation of a biofilm, bacterial cells that are free to move passively or actively through bodily fluids (i.e., planktonic bacteria), first attach to a surface (typically, damaged tissue or implanted medical devices), secrete a matrix of exopolymeric substance (EPS) that encase and protect the bacteria, and mature to form heterogeneous communities of microorganisms that are resistant to antibiotics and host defenses. The biofilm community is dynamic, and after maturation, clusters or individual cells detach and spread throughout the body (O'Toole et al., Ann. Rev. Microbiol., 54, 49 (2000)).
The bacteria in a bio film tend to be more virulent and resistant to treatment than the same bacteria in the planktonic form. For example, methicillin-resistant Staphylococcus aureus biofilms are up to 1,000 times more resistant to vancomycin than when they are grown as a planktonic suspension (Jefferson et al., Antimicrob Agents Chemother, 49, 2467 (2005)). The heightened virulence and resistance to treatment is believed to be predominantly mediated by the EPS matrix. In addition, host immunity is compromised during biofilm infections because the immune system actively works to fight the infection but is incapable of resolving the infection (Leid et al., Infect. Immun., 70, 6339 (2002); Jesaitis et al., J. Immunol., 171, 4329 (2003); Leid et al., J. Immunol., 175, 7512 (2005); Brady et al., Infect. Immun., 74, 3415 (2006)).
The infected body part is typically an internal organ, such as a heart valve, vein, stomach, urinary tract, sinus, gum, bone, or joint. These infections will typically persist and often worsen over time with highly malignant results. These infections can range from subacute conditions, such as boils, kidney stones, middle-ear infections, and gingivitis, to more life-threatening illnesses, such as osteomyelitis, endocarditis, pneumonia, periodontal disease, urinary tract infections, medical device failure, and cystic fibrosis infections (Shirtliff et al., Chem. Biol., 9, 859, (2002); Parsek and Singh, Annu. Rev. Microbiol., 57, 677 (2003); Mack et al., Int. J. Art Organs, 29, 343 (2006); and Sanderson et al., Laryngoscope, 116, 1121 (2006)).
Biofilm infections are problematic in hospitals and contribute to the morbidity and mortality of immunocompromised patients. A significant number of biofilm infections are nocosomial, i.e., hospital-acquired. In particular, biofilm infections are often associated with indwelling medical devices, such as catheters, endrotracheal tubes, surgical sutures, hip and knee joint prostheses, and dental implants. Resolution is often achieved by invasive and often painful methods, such as debridement of the infected tissue or device.
Diagnosis of biofilm infections is currently accomplished by a variety of testing methods, none of which are specific for the biofilm mode of growth. For example, elevated white blood cell counts and C-reactive protein levels may indicate the presence of a biofilm infection since these are indicators of inflammation. However, these tests are incapable of determining the presence of a biofilm infection with a high level of assurance (Trampuz and Zimmerli, Injury, 37, S59 (2006)). Indeed, these tests lack the specificity required for discerning the presence of a biofilm infection versus a non-biofilm infection caused by any similar microorganism.
Culturing is another common method used in identifying microorganisms that may be involved in a biofilm infection, but contamination and long processing times are common problems. The inefficiency of traditional culturing methods to correctly identify microbes is exacerbated with biofilms. For example, biofilm microorganisms are difficult or impossible to culture on standard agar plates (Veeh et al., J. Infect. Dis., 188, 519 (2003)). Even more, since biofilm organisms are inherently attached to a surface, they are not readily cultured by standard techniques which typically requires their transfer, and hence, detachment from the surface to which they are originally bound.
Serology-based assays are becoming more common since they address some of the problems associated with the culturing and imaging techniques. These in vitro assays can identify antibodies in sera that are active against one or more microorganisms that may be associated with a biofilm infection. The assays are typically conducted by testing serum with a test antigen believed to be indicative of the biofilm infection. Antibodies in the sera are typically tagged with a marker (e.g., fluorophore or nanoparticle) so that any antibodies that bind to the test antigen are readily observable on a substrate. However, at least one significant drawback of the assay technique is that determination of the presence of a microorganism does not necessarily indicate the active presence of a biofilm infection. A microorganism can be present in sera for several reasons other than due to a biofilm infection. For example, S. aureus is a highly ubiquitous pathogen which is often detected in serology-based assays as a false positive, because the antigen used is not indicative of the biofilm mode of growth. In addition, even if a serology-based assay can firmly establish the presence of a biofilm infection, this information is highly limited in that it generally does not provide information on the location or extent of the infection. Yet, knowing the location and extent of the biofilm infection is critical in determining a course of treatment.
Accordingly, there remains a need in the art for new, rapid, and inexpensive techniques to diagnose biofilm infections in patients. There is a particular need for in vivo diagnostic tests that can rapidly provide information on the precise location and severity of the infection. The diagnostic test would also preferably be easily incorporable into standard hospital equipment and procedures.